1. Field of the Invention
This invention relates to leak testers used for defect tests of iron wheels and aluminum wheels of automobiles, for example. Particularly, this invention relates to leak testers which are capable of performing leak tests on multiple kinds of works, having different diameters, with a long life.
This application is based on Patent Application No. Hei 10-248760 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, engineers use leak testers for inspecting casting defects of iron wheels and aluminum wheels (hereinafter, simply referred to as "wheels") of automobiles, for example. FIG. 4 is a schematic illustration showing an example of a leak tester conventionally known. The leak tester of FIG. 4 is basically constructed by a base 24, a bell jar 25, and a chamber 21. Herein, the bell jar 25 is capable of moving up and down on the base 24 by way of chamber seals 32, such as O-rings. A pipe 31a is arranged beneath the base 24 to introduce trace gas into the chamber 21. Herein, the pipe 31a penetrates through an introduction opening 22 of the base 24 to communicate with the chamber 21. A pipe 31b is arranged on an upper surface of the bell jar 25 to lead "leaked" trace gas, leaked in an inside of the chamber 21, to a detector. The pipe 31b penetrates through a detection opening 23 of the bell jar 25 to communicate with the chamber 21. A support rod 26 is inserted into a center hole of an upper portion of the bell jar 25 by way of a seal 33, such as an O-ring. An end portion of the support rod 26 is interconnected to a work press plate 27 in the chamber 21. Upper seals 28 having ring-like shapes are fixed to a lower surface of the work press plate 27. In addition, lower seals 29 having ring-like shapes are fixed to an upper surface of the base 24. As the seals 28 and 29, it is possible to use plate rubber materials, which are cut in ring-like shapes.
A work (30) is supplied to the aforementioned leak tester, as follows:
First, a human operator (or worker) inserts a plug into a valve hole of a wheel, which serves as a work, by fingers. Then, the human operator moves the bell jar 25 upward to open the chamber 21 and pull up the work press plate 27. The work 30 is arranged between the upper seals 28 and the lower seals 29. Such arrangement of the work 30 is performed manually or automatically by using a robot, for example. Thereafter, the work press plate 27 is forced to descend down, so that rims 34 of the work 30 are tightly sandwiched between the upper seals 28 and the lower seals 29. At the same time, the bell jar 25 is forced to descend down, so that the chamber 21 is closed. FIG. 5 is a schematic illustration showing a contact state established between the lower seal 29 and the rim 34 of the work 30. Due to compressive force being supplied from the work press plate 27, the rim 34 is pressed against the lower seal 29. Thus, the lower seal 29 partially becomes depressed at a contact area, surrounding areas of which are forced to rise.
After completion in arrangement of the work 30 in the leak tester, the leak tester evacuates air, which exists inside of the work 30, from the introduction opening 22 by way of the pipe 31a. Then, the leak tester introduces trace gas such as helium gas into the work 30 from the introduction opening 22 by way of the pipe 31a. At the same time, the detector detects gas, which exists inside of the chamber 21 and which is lead thereto from the detection opening 23 by way of the pipe 31b. If the work 30 has a defect, the trace gas leaks from the inside of the work 30, so that the chamber 21 will be filled with the trace gas. The detector detects the leaked trace gas. Thus, it is possible to detect existence of the defect and a size of the defect.
After completion of the test, the leak tester evacuates the trace gas from the work 30, while air is flown into to chamber 21. Then, the human operator takes the inserted plug by fingers and pulls it out from the valve hole. Thereafter, the human operator installs the next work having a valve hole into which a plug is inserted in the chamber 21. Thus, it is possible to proceed to testing of the next work.
In the conventional leak tester described above, the work 30 is sealed while being sandwiched between the upper seals 28 and the lower seals 29. So, compressive force is locally imparted to the upper seals 28 and the lower seals 29. However, the conventional leak tester does not provide a support which supports the upper seals 28 and the lower seals 29 from their peripherals. For this reason, the upper seals 28 and the lower seals 29 must be noticeably deformed. That is, as shown in FIG. 5, the upper seal 29 (and the lower seal 28) becomes partially depressed at the contact area, surrounding areas of which swell up. When the work is changed with another work having a different diameter, a position that compressive force affects changes as well, so an area of the seal being deformed is correspondingly changed. If such deformation repeatedly occurs, surfaces of the seals 28 and 29 must be abraded so as to cause formation of cracks. In that case, there is a problem that the leak test cannot be performed.
In addition, the surfaces of the lower seals 29 are formed like flat planes. So, when the work 30 is installed into the leak tester or when the work 30 is sandwiched between the seals, the work 30 is easily changed in location. That is, it is difficult to automatize supply process or removal process of the work 30.
Further, when the plug is inserted into the valve hole of the wheel, the human operator uses his or her fingers to insert or extract it. Such manual operations for insertion and extraction are not good in work efficiency. Once the air is evacuated from the work so that the inside of the work is placed in a decompressed state, the plug must be tightly attached to the work. In that case, a large force is required to extract the plug from the work. However, it is difficult to apply sufficient extraction force to the plug by fingers. In addition, reliability of the leak test is reduced due to abrasion of the plug.